In systems using flexible media, specifically the so-called "floppy disc" systems, the media is confined within an envelope so that it can be stored, handled, mailed, and conveniently inserted into and removed from the floppy disc drive. The envelope has openings for different purposes, including a central opening exposing the central aperture of the compliant magnetic disc. The floppy disc drives are configured so that, when the disc is inserted into operative position, a member on one side of it can engage the central part of the disc against a rotatable spindle on the other, clamping the disc between the members and thus rotating the disc with the spindle, so that recording and reproduction can be accomplished.
In the earliest forms of floppy disc drives, as evidenced by Dalziel U.S. Pat. No. 3,678,481, the clamp and drive arrangement used a solid conical element to fit within the central aperture of the floppy disc. The conical element penetrated within a central concavity in the spindle, centering the disc concurrently with clamping, by moving the conical member into an engaged position. This arrangement was generally satisfactory for initial systems, in which relatively wide tracks (e.g. 12 mils) at relatively low track density (e.g. 48 tracks per inch) were utilized.
There has since been considerable attention directed toward improving the positioning and clamping structures for floppy disc mechanisms, as evidenced by U.S. Pat. Nos. 4,125,883 to Rolph, 4,208,682 to Bryer and 4,171,531 to Grapes et al, and the patents cited therein. As the art has evolved, the positioner cone, generally a plastic element, has been segmented radially into a number of petals or leaves, which are arranged to be somewhat resilient in order to be clamped down but substantially stiffer than the deformation characteristics of the floppy disc. There is a wide range of different approaches to the problem, as evidenced by the various patents, because the problem is not a simple one. The problems become more complex as the track widths become smaller (e.g. 4 to 6 mils) and the track density is doubled (e.g. 96 to 100 tpi). Under these conditions, expectable variations in the diametral size of the central aperture of the floppy disc, edge deformation on the floppy disc, and variations in the positioner cone itself, limit the degree to which eccentricity of the floppy disc about the central axis can be limited.
When a higher degree of precision is required in centering a floppy disc, other aspects also come into play. In most systems the positioner cone is mounted on the floppy disc cover, or on a pivotable support structure, so that as the cone is lowered down onto the disc and then engages the spindle it follows an arcuate path. Entry of the positioner cone into the central aperture of the floppy disc in this manner is undesirable, inasmuch it can bend an edge of the aperture upon entry, or otherwise cause loss of precise centering.
The state of the art is evidenced by a structure disclosed in U.S. Pat. No. 4,139,876 to Owens in which the positioner cone is retained in a pivotable frame that can be moved downwardly to engage the positioner cone against a spindle. In practice the cone is segmented into relatively stiff petals, whose outline is smaller than the disc aperture. After the cone is seated on the spindle, clamping the floppy disc, a follower cone acts to spread the petals apart, attempting to urge them apart to attempt to center the floppy disc. The pivotal mounting of the positioner cone causes it to move into the aperture in the floppy disc along an arc, giving rise to the problems mentioned above.